This commit removes the verbose options from the gate job and disables
clamav installation in the CI jobs. The clamav package is only available
in the EPEL repository, but the EPEL repo has been removed from
the CentOS images in the OpenStack gate. This will need to be handled
carefully in a later patch.
It also removes an apostrophe from `tasks/main.yml` that breaks syntax
highlighting in vim.
Change-Id: Ifbfc56ed5fe92887cf5beb6b2703fdc3e1c8bb05
5ef94bf0ca